Helmets are general head gear for a variety of mobile vehicles users, including from bicyclists, motorcyclists, pilots, etc. Generally, professional and military pilots of rotary-winged and fixed-winged aircraft have personally fitted helmets. Due to variation in body dimensions, such as different head size or eye location, attachments to the helmet which require precise positioning are custom fitted per pilot at the time of usage.
Among the attachments which require precise positioning are optical systems, such as night vision goggles and helmet mounted displays. In general, eye levels usually vary both horizontally and vertically; the inter-pupilary distance (IPD) (the distance between the two eyes) varies from between 52 to 72 mm, and the frontal position (the distance from the helmet edge to the eye line) varies by a similar range. Both these variants are products of varying head shape and size.
To date, helmet mounted displays are mounted onto the helmet by one of two methods. Option one entails an optical unit permanently mounted onto the helmet. In such a case, the optical unit id designed large enough to fit most users, and hence is usually excessively large and heavy.
The second option is to use a removable adaptable optical unit which is mounted onto the helmet before use and then adjusted to the personal dimensions of each user. This option, however, requires readjusting and repositioning the optical unit each and every time the optical unit is removed from the helmet of one user and remounted onto the helmet of another, as is frequently done with military platforms. Since it is common practice for one pilot to step out of the cockpit while another waits to get in, this time consuming procedure is routinely carried out numerous times per day.
An additional disadvantage of the removable adaptable optical unit is the excessive wear and tear on the connecting elements. If the connecting elements are produced to meet light weight requirements, they wear quickly; if the elements are produced to withstand constant removal, they generally are exceedingly heavy for comfortable wear.
Night vision goggles have an added difficulty. In order to produce a light weight unit, most night vision goggles have numerous plastic parts, such as plastic screws. The plastic parts are not especially durable under multiple adjustments and stresses, and deteriorate with each remount and subsequent readjustment of the system.
Two examples of prior art helmet mounted systems are described in EPO patent 0675692 B1 and French patent application 268866, both of which describe adjustable helmet mounted optical systems.